Stability Phase Diagram of YBa$_{2} \text{Cu}_{3}\text{O}_{\text{7-}\delta}$ for the Composition of Y:Ba:Cu = 1:1:2.5 in Low Oxygen Pressures

We report the stability phase diagram of YBa
₂
Cu
₃
O
_7-δ
(YBCO) in low oxygen pressures (PO
₂
) for the composition of Y:Ba:Cu = 1:1:2.5. For this study, the Y-Ba-Cu-O amorphous precursor films, deposited on LaAlO
₃
(001) substrates by pulsed laser deposition, were annealed at various high temperatures in the low PO
₂
region of 1-150 mTorr, and then rapidly quenched to room temperature using a reel-to-reel tube furnace. Compared with the stability phase diagram of the stoichiometric YBCO compound, the stability boundary of YBCO for this composition was significantly shifted to the lower temperature. More interestingly, above the stability boundary of YBCO, while Y
₂
BaCuO
₅
(Y211) + YBa
₃
Cu
₂
Oy (Y132) + liquid (L) or Y
₂
O
₃
+ Y132 + L are stable equilibrium phases for the stoichiometric YBCO compound, Y
₂
O
₃
+ L are stable ones for this composition, suggesting that YBCO coated conductors can be fabricated via the reactive coevaporation deposition and reaction process from this nominal composition.